On high-speed diesel return-line extrusion lines, Arkema Rilsan BESHV BLK T PA11 is introduced as a pre-compounded black, heat-stabilized high-viscosity polyamide 11. The processing window is narrower than for lower-viscosity PA11 grades because the black concentrate raises melt viscosity and can mask early signs of thermal shear. A representative profile on a 45 mm single-screw extruder with an L/D ratio of 30:1 and a barrier screw having a compression ratio of 2.5:1 is used. The feed throat is kept below 60 °C to prevent pellet bridging. The barrel profile from zone 1 to zone 4 is set at 225 °C, 235 °C, 240 °C, and 245 °C; the adapter and die are set at 250 °C. Melt temperature at the die entry should not exceed 255 °C during steady-state production. Because the grade is high-viscosity, pressure generation at 80 rpm screw speed can vary by ±15 % between lots; a gear pump is therefore installed to stabilize die pressure within ±0.3 MPa. Filter packs with 60/80/120 mesh screens are used before the breaker plate to trap carbon black agglomerates larger than 40 µm. The pellets are dried at 80–90 °C for 4–6 h in a desiccant dryer with a dew point of −40 °C to a moisture content below 0.08 %. At 0.12 % moisture, the extrudate shows splay, the melt strength falls, and the inside diameter of the tube loses concentricity. Surfaces are inspected for haze and die-lip plate-out; both indicate either moisture or local residence time above 260 °C at the screw tip. The finished product is a diesel return line in outside diameters from 4 mm to 8 mm, qualified against OEM hydrocarbon-resistant tubing specifications and, where invoked, SAE J2260. The raw-material lot certificate is compared against the ISO 1874-1 PA11-HIP classification for viscosity and heat stability.

What Limits the Burst Pressure Window in SAE J844 Air Brake Coiled Tubing?

Air brake coiled tube made from Rilsan BESHV BLK T PA11 is extruded to outside diameters of 6.35 mm, 9.52 mm, and 12.70 mm with wall thicknesses from 1.0 mm to 1.5 mm. The governing document is SAE J844 for non-reinforced nylon tubing. The limiting process variable is not barrel temperature but residual stress created by in-line coiling. If the tube is coiled under excessive tension without controlled air quenching, the inner radius of the coil can develop micro-kinks that act as burst-initiation sites. Vacuum sizing is run with a closed-loop vacuum of −0.06 MPa to −0.08 MPa; a calibration sleeve is dimensioned 0.15 mm larger than the final outside diameter to compensate for post-crystallization shrinkage. The heat-stabilized black grade is suited to trailer and underbody lines where UV exposure and residual engine heat coexist. The critical qualification step is oven aging at 100 °C for 72 h, followed by burst testing at 23 °C and −40 °C in accordance with SAE J844. During fitting assembly, brass compression fittings impose a long-term hoop stress; the stabilizer package retards oxidative chain scission at the fitting edge. Hot air and oil mist from compressor discharge are additional oxidative loadings that are addressed by the heat-stabilized additive system. The process boundary is strict: melt residence time above 260 °C must remain below 5 min, or the melted black PA11 begins to generate gel particles at the die lip. Finished coils are conditioned at 50 % RH for 24 h before burst qualification because moisture equilibrates the local notch sensitivity of the polyamide and reduces scattered low-temperature failures.

Unbonded flexible risers require a polyamide pressure sheath that retains ductility after exposure to formation water, methanol, and aromatic hydrocarbons. Rilsan BESHV BLK T PA11 is used as a thick-walled pressure sheath over the metallic carcass when the design temperature is inside the PA11 compatibility envelope defined by API 17J and ISO 13628-2. The extrusion is performed on a heavy-duty single-screw extruder with a 90 mm to 150 mm screw diameter and an L/D ratio of 28:1 to 33:1. The melt temperature at the die is maintained between 230 °C and 245 °C; the thick wall increases the residence time of the inner surface at elevated temperature during cooling, so the screw speed is reduced to keep the average melt temperature below 250 °C. The high melt strength of the BESHV class prevents sagging before the water quench. Wall thickness is controlled by a non-contact ultrasonic gauge that records thickness profiles around the circumference; any point below the specified minimum, often 5.0 mm, triggers automatic line slowdown. The main process conflict is residual stress: thick PA11 sheaths cool from the outside inward, and the inner surface can remain above 120 °C for several minutes. Forced water cooling from both outside and inside is required for wall thicknesses above 8 mm. When tested to ISO 62, typical unfilled PA11 absorbs less water than PA6 or PA66 under equivalent conditions, which reduces swelling-induced dimensional change, but hydrolysis still occurs in sour production fluids. The design envelope therefore requires compatibility testing of the grade with the specific produced-fluid composition, including H₂S partial pressure and methanol content. Published data for BESHV BLK T in highly sour configurations is limited; long-term hydrostatic testing is conducted at 23 °C, 40 °C, and 60 °C on end fittings. The final part is a seamless pressure sheath in unbonded flexible risers or flowlines for subsea tie-backs.

When a PA11 Barrier Layer Is Co-Extruded Below an EVOH Core in Low-Permeation Fuel Filler Lines

In low-permeation fuel filler lines, Rilsan BESHV BLK T PA11 is co-extruded as a hydrocarbon contact layer below an EVOH barrier core. The design is driven by evaporative emission limits under 40 CFR Part 86 or CARB LEV III, depending on the vehicle platform. A representative wall structure places the PA11 inner layer at 20 wt% of total wall thickness, the EVOH core below 10 wt%, and the outside PA12 or PA6 layer at the balance. Tie layers are required to prevent delamination because EVOH does not fuse directly to PA11 under shear. The co-extrusion line uses five extruders with sequential layer distribution; the PA11 extruder is run from 210 °C to 235 °C at the die, while the EVOH extruder is kept below 220 °C to prevent gas formation. The black PA11 layer must not be assumed to be antistatic; surface resistivity is verified with IEC 61340-2-3 when the OEM specifies a conductive inner surface. If the measured surface resistivity exceeds the required limit, a dedicated conductive PA11 grade is substituted for the inner skin. The critical process risk is interfacial instability: differences in melt viscosity between PA11 and EVOH produce wavy layer boundaries at the die exit. The correction is to balance layer viscosities and use a spiral mandrel die with sufficient distribution volume. The final product is cut and welded into a fuel filler line assembly; heat-stabilized PA11 maintains hoop strength after underbody heat aging at 125 °C for 1,000 h in internal validation programs. The material lot is released against ISO 527-1/-2 for tensile elongation and ISO 178 for flexural modulus; the minimum elongation after aging is set by the end-user specification, not by a generic PA11 value. Permeation testing is referenced to SAE J1737 where the OEM specification invokes a low-hydrocarbon-leakage construction.

Vacuum Corrugator Output Stability Depends on Melt Strength, Not Line Speed Alone

Convoluted cable protection conduit produced from Rilsan BESHV BLK T PA11 is formed on a vacuum corrugator after a short post-die air gap. The process is more sensitive to melt strength than to line speed. The high-viscosity polyamide is extruded through a tube die with a die gap of 0.8 mm to 1.2 mm and is then pulled into a moving mold block. The vacuum in the mold block is maintained between −0.04 MPa and −0.07 MPa. If the vacuum is excessive, the softened parison collapses into the corrugator gaps; if insufficient, the shoulder of the corrugation loses definition. Water-cooled mold blocks at 15 °C to 25 °C are used to freeze the profile before release. The black grade provides UV resistance for outdoor cable protection without an additional coating. Compliance is checked against REACH 1907/2006 and RoHS 2011/65/EU for electrical-enclosure accessories. The major failure mode is environmental stress cracking when the conduit is installed with PVC adhesive tape; the PA11 grade resists zinc chloride and is used to replace PVC conduits in rail car cable routing. The final product is supplied in coils or cut lengths with an inside diameter from 10 mm to 50 mm. Published data for BESHV BLK T specifically in convoluted conduit is limited; the processing window is therefore established on the line by adjusting melt temperature between 225 °C and 245 °C to hold a uniform parison wall.

Pre-drying control, rather than screw speed, determines the surface finish of small-diameter pneumatic control lines made from Rilsan BESHV BLK T PA11. The lines are extruded as 4 mm to 6 mm outside-diameter tubes with wall thickness of 0.5 mm to 1.0 mm for automated assembly cells. The resin is dried to below 0.06 % moisture in a desiccant dryer. A 32 mm or 45 mm single-screw extruder is run with a melt temperature of 235 °C to 250 °C. The die is a straight in-line head with a 0.8 mm mandrel gap; vacuum calibration is replaced by pressure sizing at 0.05 MPa for line speeds below 30 m/min. Each coil is tested online with dry air at 1.0 MPa and cut to length. The critical incompatibility is contact with formaldehyde-based machining coolants; these fluids are kept off the tube because they can accelerate surface attack. The final product is stored in moisture-barrier film to prevent moisture regain before installation.